This invention relates to a flying spot scanning system for communicating video information to or reading information from a scanned medium, and more particularly to a scanning system which utilizes a symmetrical arrangement of reflective surfaces between the scanning element and the scanned medium for field flattening.
Much attention has been given to various optical approaches in flying spot scanning for the purpose of imparting the information content of a modulated light beam to a scanned medium. Galvanometer arrangements have been used to scan the light across a document for recording its information content thereon. Such arrangements have included planar reflecting mirrors which are driven in an oscillatory fashion. Other approaches have made use of multifaceted mirrors which are driven continuously. Various efforts have been made to define the spot size in order to provide for an optimum utilization of the scanning system.
One such effort is that described in U.S. Pat. No. 3,675,016. The approach used was to make the spot size invariant and as small as possible by defining the dimensions of the focused beam so that only part, preferably half, of a mirror facet is illuminated during scanning. This teaching alludes to generalized techniques for assuring the constancy of the size of the aperture of a rotating mirror scanning system.
Other approaches, such as that taught in U.S. Pat. application Ser. No. 488,332, filed on July 15, 1974, and assigned to the assignee of the present invention, have sought to assure a uniform spot size at the scanned medium. A convolution of focusing elements may be selected, for example, to provide an adequate depth of focus at the planar surface of the medium to compensate for focal plane errors due to the arcuate path of the scanned spot.
The present invention offers still another approach to the avoidance of focal plane error.
It is thus an object of the present invention to provide a flying spot scanning system which avoids focal plane error.
It is yet another object of the present invention to provide a spot scanning system which provides an effective uniform spot size at the contract loci of the spot with the scanned medium.
It is a further object of the present invention to provide a spot scanning system which utilizes symmetrical reflective surfaces for reducing the effective scan angle of the directed light beam.
Other objects of the invention will be evident from the description hereinafter presented.